Handy solar info for lead acid batteries

Your 24V panels are not "true" 24V panels. A true 24V panel has 2 * 36 cells. You have less. That means the cliff where current drops is more to the left, at a lower voltage. Add the effect of temperature and your 24V pwm controller will have problems at higher temperature.

BFL13 wrote:

Since PWM uses Isc, which does not go down with temperature, you don't care about panel temp with PWM, but it hurts MPPT big time.